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Shorten IPv6 addresses for display

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original commit: cf4c71a51f
This commit is contained in:
Asumu Takikawa 2013-03-02 12:53:35 -05:00
parent 0f309cd525
commit a49b615b9a
1 changed files with 28 additions and 4 deletions
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32
collects/net/dns.rkt
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@ -5,6 +5,7 @@
(require racket/bool (require racket/bool
racket/contract racket/contract
racket/format racket/format
racket/list
racket/match racket/match
racket/string racket/string
racket/system racket/system
@ -356,13 +357,36 @@
;; Convert a list of bytes representing an IPv6 address to a string ;; Convert a list of bytes representing an IPv6 address to a string
(define (ipv6->string lob) (define (ipv6->string lob)
(define two-octet-strings (define two-octets
(for/list ([oct-pair (in-slice 2 (in-list lob))]) (for/list ([oct-pair (in-slice 2 (in-list lob))])
(define oct1 (car oct-pair)) (define oct1 (car oct-pair))
(define oct2 (cadr oct-pair)) (define oct2 (cadr oct-pair))
(~r (+ (arithmetic-shift oct1 8) oct2) (+ (arithmetic-shift oct1 8) oct2)))
#:base 16))) (define compressed (compress two-octets))
(string-join two-octet-strings ":")) (define compressed-strs
(for/list ([elem compressed])
(if (eq? elem '::)
"" ; string-join will turn this into ::
(~r elem #:base 16))))
(string-join compressed-strs ":"))
;; (Listof Number) -> (Listof (U Number '::))
;; Compress an IPv6 address to its shortest representation
(define (compress lon)
(let loop ([acc '()] [lon lon])
(cond [(empty? lon) (reverse acc)]
[else
(define zeroes (for/list ([n lon] #:break (not (zero? n))) n))
(define num-zs (length zeroes))
(if (<= num-zs 1)
(loop (cons (car lon) acc) (cdr lon))
(append (reverse acc) '(::) (drop lon num-zs)))])))
(module+ test
(check-equal? (compress '(0 0 0 5 5)) '(:: 5 5))
(check-equal? (compress '(0 5 5)) '(0 5 5))
(check-equal? (compress '(0 0 5 0 0 5)) '(:: 5 0 0 5))
(check-equal? (compress '(0 5 0 0 0 5)) '(0 5 :: 5)))
;; (NameServer -> (Values Any LB Boolean)) NameServer -> Any ;; (NameServer -> (Values Any LB Boolean)) NameServer -> Any
;; Run the given query function, trying until an answer is found ;; Run the given query function, trying until an answer is found